Submarine Cable Interface For Connection to Terrestrial Terminals

ABSTRACT

In an optical network having a terrestrial terminal and an open cable interface (OCI) connecting a submarine cable to a terrestrial cable, the OCI may include a filter positioned on an optical path between the terrestrial cable and the submarine cable and configured to pass first communication signals of a first frequency band, and filter out secondary signals of a second frequency band that does not overlap with the first frequency band. The secondary signals may be looped back to the terrestrial terminal. The terrestrial terminal may detect the looped back secondary signals, and in response, determine the presence of the OCI and that the supervisory signals were rerouted by the OCI.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.17/220,526, filed on Apr. 1, 2021, the disclosure of which isincorporated herein by reference.

BACKGROUND

Communication networks include both terrestrial optical cables to carryoptical communication signals over land, and submarine optical cables tocarry the optical communication signals across large bodies of waterbetween land masses. In a typical scenario, the signals from aterrestrial network are not compatible with those from a submarinenetwork. The signals of the respective networks may differ in terms offrequency ranges, modulation formats of the data channels, and both typeand quality of supervisory channels for system telemetry, control, andoperations.

In order to interface the terrestrial cables with the submarine cablesto create an interconnected optical network, conventional opticalnetwork systems include specialized equipment. This specializedequipment for facilitating this interface is commonly termed submarineline terminal equipment (SLTE). SLTE generate the signals that aretransmitted across submarine cables. For instance, SLTE include thecomponents for multiplexing optical wavelengths, adjusting power levelsof optical signals, filtering parts of the optical spectrum, loading thesubmarine cables with noise in some regions of the spectrum, and so on.

However, the use of specialized and dedicated SLTE to interface thesubmarine network with the terrestrial network is costly and burdensome.Having to produce specialized terrestrial equipment, as compared to onlyproducing standard terrestrial equipment, adds significant cost to theoverall system. Furthermore, installation of standard terrestrialequipment is cheap and straightforward, but installation of SLTE isexpensive because it requires a skilled technician to manually calibratepower levels of the equipment so that it operates correctly, such as byinserting a patch cord or creating an offset splice in order to add adesired amount of residual attenuation. Additionally, the differencesbetween standard terrestrial equipment and SLTE necessitate assigningdifferent stock keeping units (SKUs) to each type of terminal. This, inturn, requires tracking and managing an extra SKU in order to maintainthe network, which adds undue time and cost to the maintenance process.

BRIEF SUMMARY

The present disclosure avoids the need for specialized SLTE at theinterface with the submarine cables. This is accomplished by providingan optical cable interface (OCI) between the submarine cable and astandard terrestrial cable with a filter to filter out signals withfrequencies outside of the allowed frequency range for submarinesystems. The OCI may further be configured to loop the filtered outsignals back towards the terrestrial cable network, which may be used toindicate the presence of an interface between a terrestrial opticalcable and a submarine optical cable to control circuitry in theterrestrial optical network.

One aspect of the present disclosure is directed to an open cableinterface (OCI) configured to connect a submarine cable to a terrestrialcable of an optical network, the open cable interface comprising: afirst optical path configured to provide first communication signalsfrom the optical network to the submarine cable; and a second opticalpath configured to provide second communication signals from thesubmarine cable to the optical network, wherein the first and secondcommunication signals are within a first frequency band; and a firstfilter positioned on the first optical path and configured to: pass thefirst communication signals; and filter out secondary signals from theterrestrial cable, wherein the secondary signals are within a secondfrequency band that does not overlap with the first frequency band.

In some examples, the second frequency band may include at least one of1510 nm or 1610 nm.

In some examples, the first filter may be a wavelength divisionmultiplexing (WDM) filter.

In some examples, the secondary signals may include an opticalsupervisory channel signal.

In some examples, the secondary signals may include an opticaltime-domain reflectometry signal.

In some examples, the OCI may include a second filter positioned on thesecond optical path and configured to pass the second communicationsignals from the submarine cable to the terrestrial cable, and the firstand second filters may be configured to loop the secondary signalsreceived from the terrestrial cable back to the terrestrial cable.

In some examples, the OCI may include a first variable opticalattenuator (VOA) positioned on the first optical path between the firstfilter and the submarine cable and configured to adjust a power level ofthe first communication signals without affecting a power level of thesecondary signals.

In some examples, the OCI may include a second VOA positioned on thesecond optical path between the second filter and the submarine cable.

In some examples, the OCI may be configured to connect to a terrestrialtransmission equipment having a same stock keeping unit (SKU) as otherequipment included in the optical network that do not interfacesubmarine cables.

In some examples, the terrestrial cable may have a same SKU as otherterrestrial cables included in the optical network.

Another aspect of the disclosure is directed to a system comprising: oneor more processors; and memory in communication with the one or moreprocessors and containing instructions configured to cause the one ormore processors to: transmit a supervisory signal from a terminal of aterrestrial optical cable of a terrestrial network; detect thesupervisory signal being reflected back to the terminal; in response todetection of the supervisory signal being reflected back to theterminal, determining that the supervisory signal was rerouted by anoptical cable interface to a submarine cable.

In some examples, the instructions may be further configured to causethe one or more processors to, in response to determining that thesupervisory signal was rerouted by an optical cable interface to asubmarine cable, initiate a power reduction program configured tomaintain power levels of transmissions to the submarine cable at orbelow a predetermined power level.

In some examples, the instructions may be further configured to causethe one or more processors to: monitor a power level of a communicationsignal passed through a WDM filter of the OCI; and in response todetermining that the supervisory signal was rerouted by an optical cableinterface to a submarine cable, adjust a power level of thecommunication signal to at or below the predetermined submarine cablepower level.

In some examples, the instructions may be further configured to causethe one or more processors to, in response to determining that thesupervisory signal was rerouted by an optical cable interface to asubmarine cable: set a travel distance of the supervisory signal fromthe terminal to the optical cable interface and back to the firstterminal as twice a distance between the terminal and the optical cableinterface; and evaluate travel time of supervisory signals transmittedfrom the terminal to the optical cable interface based on the set traveldistance.

In some examples, the instructions may be further configured to causethe one or more processors to, in response to determining that thesupervisory signal was rerouted by an optical cable interface to asubmarine cable: determine a loss in supervisory signals transmittedfrom the terminal to the OCI and back to first terminal; and estimate anactual loss of supervisory signals transmitted from the terminal to theOCI to be half of the determined loss.

Yet another aspect of the disclosure is directed to an optical networkcomprising: a plurality of terrestrial optical cable terminals,including a first terrestrial optical cable terminal interfacing anoptical cable interface to a submarine cable and a second terrestrialoptical cable terminal that does not interface an optical cableinterface to a submarine optical cable; and a system as described in anyof the embodiments herein.

In some examples, the first terrestrial optical cable terminal and thesecond terrestrial optical cable terminal may have a common SKU.

Yet a further aspect of the disclosure is directed to a methodcomprising: transmitting, by one or more processors, a supervisorysignal from a terminal of a terrestrial optical cable of a terrestrialnetwork; detecting, by the one or more processors, the supervisorysignal being reflected back to the terminal; and in response todetection of the supervisory signal being reflected back to theterminal, determining, by the one or more processors, that thesupervisory signal was rerouted by an optical cable interface to asubmarine cable.

In some examples, the method may be performed during initialization of asupervisory program for monitoring signals transmitted over theterrestrial network.

In some examples, the method may further include, in response todetermining that the supervisory signal was rerouted by an optical cableinterface to a submarine cable, activating a submarine cable use case.The submarine cable use case may include one or more of the following:reducing a power level of communication signals transmitted from theterminal towards the OCI to a predetermined submarine cable power levelor below; evaluating a travel time of a supervisory signal transmittedfrom the terminal towards the OCI as a round trip time; or evaluating aloss of the supervisory signal transmitted from the terminal towards theOCI to be half of a measured loss at the terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an optical network according to aspectsof the disclosure.

FIGS. 2A and 2B are schematic diagrams of example open cable interfaces(OCI) according to aspects of the disclosure.

FIG. 3 is an example block diagram of terrestrial terminal equipment(TE) according to aspects of the disclosure.

FIG. 4 is a flow diagram of an example routine according to aspects ofthe disclosure.

DETAILED DESCRIPTION Overview

The present disclosure relates generally to devices and methods forinterfacing a terrestrial optical network and a submarine opticalnetwork without specialized SLTE. Specifically, an OCI including afilter is positioned along a first optical communication path of the OCIfrom a terrestrial cable to a submarine cable. The filter is capable ofpassing communication signals within a first frequency band that iswithin the allowed frequency range for the submarine cable, whilefiltering out other signals, such as supervisory signals, that areoutside of the allowed frequency range for the submarine cable.

In some examples, the OCI may include a second filter positioned along asecond optical communication path of the OCI from the submarine cable tothe terrestrial cable. The first and second filter may be capable oflooping the filtered-out other signals back towards the terrestrialcable network. At the terrestrial cable network, the looped back signalsmay be detected by standard terminal equipment, and their detection maybe interpreted as indicating the presence of an interface between aterrestrial cable and a submarine cable. Because the presence of theinterface is detectable using the looped back signals, standard terminalequipment within the terrestrial system can control a power level of thecommunication signals within the first frequency band based on thedetection. Thus, both frequency control and power control using standardterrestrial terminal equipment are made possible by the inclusion of thefirst and second filters and a loopback path within the OCI.

In some further examples, the OCI may also include at least one variableoptical attenuator (VOA) positioned along the first opticalcommunication path between the first filter and the submarine cable. TheVOA may be responsible for adjusting the power level of thecommunication signals passed by the first filter before they arereceived at the submarine cable. Using a VOA positioned on the“submarine side” of the first filter, as opposed to attenuating elementspositioned within the terrestrial network or on the “terrestrial side”of the first filter within the OCI, is beneficial for avoidingattenuation of the other signals that are looped back to the terrestrialnetwork, especially considering that positioning attenuating elements onthe “terrestrial side” of the filters would doubly attenuate the signals(once along each path) and would potentially make detection of thelooped back signals more difficult.

Inclusion of the OCI of the present disclosure at an interface between aterrestrial optical network and a submarine optical network avoids theneed for specialized SLTE on the terrestrial side of the interface. Thisachieves a reduction in cost due to the relative low cost of standardterrestrial optical cables, as compared to SLTE. Furthermore, nohardware changes are needed to the terrestrial equipment. A softwareupdate can be provided to the standard terrestrial terminal equipment inorder to detect locations of the terrestrial network that interface withsubmarine cables based on supervisory signals that loop back towards thestandard terrestrial terminals. Additionally, when allterrestrial/submarine interfaces in the optical network are outfittedwith the OCI of the present disclosure, a single SKU can be used for allterminal equipment of the entire network.

Example Systems

FIG. 1 is a schematic diagram of an optical network 100 including afirst terrestrial optical network 102 and a second terrestrial opticalnetwork 104 connected to one another by a submarine optical network 106.For instance, each of the terrestrial optical networks 102, 104 may besituated at landmasses A and B that are separated by a body of watersuch as sea S, and the submarine network may be situated primarily inthe sea S. The respective terrestrial networks of the landmasses A, Bmay be communicatively connected to one another via one or moresubmarine cables across the sea S.

Each of the terrestrial optical networks 102, 104 is shown to include atleast one respective terminal including terminal equipment (TE) 112, 114for receiving and transmitting communication signals through the opticalnetworks, and for monitoring operation of the optical networks. Theterminal equipment 112 of the first terrestrial optical network 102 isconnected to a first optical cable 122, and the terminal equipment 114of the second terrestrial optical network 104 is connected to a secondoptical cable 124. The first and second optical cables are connected toeach other by the submarine optical network 106. Additional terminalsand optical cables (not shown) may be included in each optical network.

The submarine optical network 106 may include one or more submarineoptical cables 130 that are connected at opposite ends to the first andsecond terrestrial optical networks 102, 104, respectively. In theexample of FIG. 1 , a first end of the one or more submarine opticalcables 130 is connected to the first optical cable 122 through a firstopen cable interface (OCI) 132, and an opposite second end of the one ormore submarine optical cables 130 is connected to the second opticalcable 124 through a second OCI 134. Furthermore, each of terminalequipment 112 and 114 may be standard terrestrial terminal equipment, ascompared to SLTE. As such, both ends of the one or more submarineoptical cables 130 may be connected to standard terrestrial terminalequipment through respective optical cables.

Each of the OCIs 132, 134 may be adapted in order to supportcompatibility between the cables of the submarine optical network 106and the terrestrial optical networks 102, 104. FIG. 2A is a schematicdiagram of an example OCI 230 for interfacing a submarine opticalnetwork with a terrestrial optical network using standard terrestrialterminal equipment 212. In the example FIG. 2A, an optical cable 214 isshown as including two optical paths: a first optical path originatingat point 222 from which the terminal equipment 212 is configured totransmit optical signals; and a second optical path ending at point 224at which the terminal equipment 212 is configured to receive opticalsignals. Together, the first and second optical paths of the opticalcable 214 facilitate bidirectional communication between the terminalequipment 212 and the OCI 230.

The optical signals transmitted and received by the terminal equipment212 may include each of communication signals and secondary signals. Thecommunication signals may include communication data, such as messagescommunicated between end terminals of the optical network. Thecommunication signals may have a first wavelength λ₁ that is within afirst frequency band supported by the submarine optical network. Thus,the communication signals may be transmitted between landmasses A, B,through the submarine optical network. The secondary signals may includetelemetry signals for monitoring operation and performance of aterrestrial optical network, such as optical supervisory channel (OSC)signals, optical time-domain reflectivity (OTDR) signals, and the like.The secondary signals may not be supported by the submarine opticalnetwork. Therefore, in order to prevent the secondary signals from beingtransmitted to or relayed through the submarine optical network, thesecondary signals may have a second wavelength λ₂ that is within asecond frequency band that does not overlap with the first frequencyband. In one example arrangement, the first frequency band may includewavelengths less than 1510 nm, and the second frequency band may includewavelengths between 1510-1610 nm. In a different example arrangement,the second frequency band may include a wavelength of 1625, such as tosupport terrestrial OTDR signals.

The use of non-overlapping frequency bands for communication signals andsecondary signals allows for the signals to be separated from oneanother using one or more filtering techniques, including but notlimited to high-pass filtering, low-pass filtering, bandpass filtering,notch filtering, and so on. In the example of FIG. 2A, a filter 232 ispositioned at the OCI 230 on the first optical path. Communicationsignals from a first terrestrial optical network λ₁(A) and secondarysignals from the first terrestrial optical network λ₂(A) are transmittedfrom point 222 towards the OCI 230. At the OCI, the filter 232 may be awavelength division multiplexing (WDM) filter, and may be configured topass the communication signals λ₁(A) and to filter out the secondarysignals λ₂(A). Thus, only the communication signals λ₁(A) that aresupported by the submarine optical network are passed to point 242 andtransmitted through the submarine optical network, while the secondarysignals λ₂(A) that are not supported are prevented from reaching thesubmarine optical network.

In another example configuration, also shown in FIG. 2A, a second filter234 is positioned at the OCI 230 on the second optical path, and anoptical loopback path 236 is provided between the first filter 232 andthe second filter 234. The first filter 232 may be configured to sendthe filtered-out secondary signals λ₂(A) to the second filter 234 viathe optical loopback path 236, and the second filter may be configuredto reflect the secondary signals λ₂(A) received from the first filter232 back to the terminal equipment 212 along the second optical path.The reflected-back or looped-back secondary signals λ₂(A) may betransmitted from the OCI 230 along the second optical path.

FIG. 2A also shows communication signals from a second terrestrialnetwork λ₁(B) being received by the OCI 230 at point 244 of the secondoptical path. These communication signals may have the same wavelengthas the communication signals from the first terrestrial optical networkλ₁(A), or may fall within the same first frequency band. Furthermore,the second filter 234 may be configured in the same or similar manner asthe first filter 232, and thus may be configured to pass thecommunication signals from the second terrestrial network λ₁(B),resulting in the communication signals along with the looped backsecondary signals λ₂(A).

In the example of FIG. 2A, power level control for communication signalsfrom the first terrestrial optical network λ₁(A) may be performed on theterrestrial side of the OCI 230, such as at the terminal equipment 212.Adjusting the signals' power level may involve adding a predeterminedattenuation to the signals, and may be performed in order for thesignals to meet power requirements of the submarine optical network.However, by performing the power level control on the terrestrial sideof the OCI 230, a power level of the secondary signals λ₂(A) is alsoaffected. Since the secondary signals λ₂(A) are not directed through thesubmarine optical network, the power level of the secondary signalsλ₂(A) does not need to be adjusted in the same manner.

FIG. 2B is a schematic diagram of another example OCI for selectivepower adjustment of communication signals without affecting secondarysignals. Like the example OCI of FIG. 2A, the OCI of FIG. 2B interfacesa submarine optical network with a terrestrial optical network usingstandard terrestrial terminal equipment. The features of FIG. 2B are thesame as for FIG. 2A, except for the addition of one or more variableoptical attenuators (VOA) along the first and second optical paths.Along the first optical path, a first VOA 252 is positioned between thefirst filter 232 and the submarine optical network. The first VOA 252may be configured to adjust a power level of the communication signalsfrom the first terrestrial optical network λ₁(A), such as by loweringthe power level in order to meet power requirements of the submarineoptical network. By positioning the first VOA 252 on the first opticalpath after the filter 232, the first VOA 252 is capable of controllingthe power level of the communication signals λ₁(A) without affecting thepower level of the secondary signals λ₂(A).

In some examples, the attenuation introduced by the first VOA 252 may bea fixed value. For instance, the value may be set during installation ofthe OCI 230, either manually or automatically. A manual approach tosetting the attenuation value is for the value to be assigned by aremote operator through a network management software interface. Anautomatic approach to setting the attenuation value is for the value tobe assigned according to an automated script or software controller. Ineither approach, the VOA 252 could include a sensor to monitor power atthe VOA 252 by routing a small predetermined fraction of the transmittedsignals to a photodetector. Measurements from the photodetector may thenbe provided to the remote operator or automated program, and in turn canbe used to determine and set the fixed attenuation of the VOA 252.

In other examples, the attenuation introduced by the first VOA 252 maybe a variable amount subject to continuous adjustments based on feedbackfrom the VOA 252. For instance, a local control loop may be providedwithin the OCI. The local control loop may include a photodetector tosense an amount of power being output through the VOA 252, and a controlmechanism such as a microcontroller to control the VOA 252 in a mannerthat reduces, and over time minimizes, a difference between a currentpower level of the VOA 252 and a preset target power level. In such anexample, the preset target power level may be determined and programmedduring the installation process.

In some examples, a second VOA 254 may also be included in the OCI 230.The second VOA 254 may be positioned along the second optical path,between the second filter 234 and the submarine optical network. Thesecond VOA 254 may be configured to control the power level of thecommunication signals λ₁(B). For example, the power level of thecommunication signals λ₁(B) may be lowered by the second VOA 254 towithin a preset level suitable for the terminal equipment 212. Suchpower adjustment may be necessary if the terminal equipment 212 ispositioned close to the OCI 230, meaning that little to no attenuationoccurs from the OCI 230 to the terminal equipment 212.

Both example arrangements of FIGS. 2A and 2B allow for passage ofcommunication signals to the submarine optical network while blockingpassage of the secondary signals. Both example arrangements also permitfor control to power levels of the communication signals prior to theirentry to submarine optical network. Both example arrangements alsopermit for the looping back of supervisory signals, which has the addedbenefit of communicating the presence of the OCI to the adjacentterminal equipment included in the terrestrial optical network, such asTE 112 of the first optical network 102 in the example of FIG. 1 . Forinstance, if a given terrestrial terminal were to transmit supervisorysignals to an adjacent node within the optical network and thesupervisory signals were received back at the same given terrestrialterminal, it could be inferred that the supervisory signals were loopedback towards the given terrestrial terminal by a filter and opticalloopback path of an OCI, thus indicating the presence of the OCI, and byextension the presence of a submarine optical network interfaced to theterrestrial optical network by the OCI. Communicating the presence ofthe OCI may be beneficial for enabling the adjacent terminal equipmentto adjust one or more settings for accommodating the nearby interface tothe submarine optical network without requiring the specialized anddedicated hardware of SLTE.

FIG. 3 is an example block diagram of standard terrestrial terminalequipment (TE). The standard terrestrial TE includes one or morecomputing devices 300 programmed with data and instructions sufficientfor transmitting supervisory signals and detecting when the supervisorysignals are rerouted or looped back towards their origin. The one ormore computing devices 300 may include a processor 310, memory 320, andone or more communication devices 350 for receiving inputs andtransmitting outputs.

The processor 310 can be a well-known processor or other lesser-knowntype of processor. Alternatively, the processor can be a dedicatedcontroller such as an ASIC.

The memory 320 can store information accessible by the processor 310including data that can be retrieved, manipulated or stored by theprocessor, instructions that can be executed by the processor, or acombination thereof. Memory may be a type of non-transitory computerreadable medium capable of storing information accessible by a processorsuch as a hard-drive, solid state drive, tape drive, optical storage,memory card, ROM, RAM, DVD, CD-ROM, write-capable, and read-onlymemories.

Although FIG. 3 functionally illustrates each of the processor 310 andmemory 320 as being a respective single block, the processor and memorymay actually include multiple processors, multiple memories, or anycombination thereof, that may or may not be stored in a common locationor within the same physical housing. For example, some or all of thedata and instructions can be stored on a removable CD-ROM and otherswithin a read-only computer chip. For further example, some or all ofthe data and instructions can be stored in a location physically remotefrom, yet still accessible by, the processor. Similarly, the processorcan actually include a collection of processors, which may or may notoperate in parallel.

The one or more communication devices may facilitate communicationbetween the terminal and other remote terminals and components of theoptical network that are in communication with the terminal. The remoteterminals and components may include terrestrial nodes of theterrestrial optical network, as well as OCIs interfacing the terrestrialoptical network to one or more submarine optical networks. Thecommunication devices may be capable of transmitting data to and fromother computers such as modems (e.g., dial-up, cable or fiber optic) andwireless interfaces. For example, each node may receive communicationsvia the network connection 130, such as through the Internet, World WideWeb, intranets, virtual private networks, wide area networks, localnetworks, private networks using communication protocols proprietary toone or more companies, Ethernet, WiFi (e.g., 702.71, 702.71b, g, n, orother such standards), and RPC, HTTP, and various combinations of theforegoing.

The memory 320 may include instructions 340, and may further includedata 330 that can be retrieved, stored or modified by the processors 310in accordance with the instructions 340. For instance, although thecomputing devices 300 disclosed herein are not limited by a particulardata structure, the data 330 can be stored in computer registers, in adata store as a structure having a plurality of different fields andrecords, or documents, or buffers. The data 330 can also be formatted ina computer-readable format such as, but not limited to, binary values,ASCII or Unicode. Moreover, the data 330 can include informationsufficient to identify relevant information, such as numbers,descriptive text, proprietary codes, pointers, references to data storedin other memories, including other network locations, or informationthat is used by a function to calculate relevant data.

The instructions 340 can be a set of instructions executed directly,such as machine code, or indirectly, such as scripts, by the processor310. In this regard, the terms “instructions,” “steps” and “programs”can be used interchangeably herein. The instructions 340 can be storedin object code format for direct processing by the processor 310, orother types of computer language including scripts or collections ofindependent source code modules that are interpreted on demand orcompiled in advance.

In the example of FIG. 3 , the data 330 stored in the memory 320 mayinclude supervisory signal data 332 indicating information about thecommunication signals and the remote conditions of one or more opticalterminals included in the network. The supervisory signal data 332 canbe used to remotely determine whether nodes and terminals of the networkare operating properly. For instance, the supervisory signal data 332may be used to detect losses, delays, or disruptions within the networkbased on supervisory data, such as feedback from remote nodes, roundtrip times, and the like. Examples of supervisory signals include butare not limited to OSC signals and OTDR signals. The supervisory signaldata 332 can further be used to facilitate remote management of thenetwork based on detected issues within the network, such as byresending or rerouting optical signals.

The data 330 may further include power level data 334 indicatingprescribed power levels for optical signals transmitted to variousterminals and nodes included in the network. For instance, the powerlevel data may indicate a first power level at which communicationsignals to adjacent terrestrial terminals should be transmitted, and asecond power level lower than the first power level at whichcommunication signals to adjacent OCIs should be transmitted.

The data 330 may further include a neighbor terminal status 336indicating respective statuses for adjacent nodes of the network. Forinstance, with regard to adjacent terrestrial terminals, the neighborterminal status of those nodes may indicate that they are terrestrialterminals. Alternatively, with regard to an OCI connected to theterminal equipment by an optical cable, the neighbor terminal status forsuch a node may indicate the presence of an OCI interfacing aneighboring submarine optical network.

The instructions 340 stored in the memory may include a supervisorysignal transmission routine 342 for transmitting supervisory signals andcollecting supervisory signal data from remote nodes of the network.

The instructions 340 may further include a terminal status check routine344 for checking the status of a given terminal, such as an adjacentterminal within the network. For instance, the terminal status checkroutine 344 may involve transmitting an optical signal having awavelength within a given range that corresponding to a wavebandfiltered by a filter of an OCI included in the network. Then, if thetransmitted optical signal is received at the transmitting terminal, itmay be determined that the signal was looped back towards the terminalby an OCI, thus indicating the presence of an interface with aneighboring submarine optical network.

The instructions 340 may further include a submarine cable use caseroutine 346 for configuring a use case of the terminal in response todetection of an interface with a neighboring submarine optical network.The submarine cable use case routine 346 may involve changing one ormore configurations of the terminal including the one or more computingdevices 300 in order for the terminal to accommodate communications withan OCI interfacing the submarine optical network to the terminal. Theconfigurations may include, but are not limited to, power levelconfigurations, supervisory signal evaluation configurations, or anycombination thereof. Some example submarine cable use cases are providedherein in connection with FIG. 4 .

Example Methods

Example routines 400 performed by the processor of one or more computingdevices of terrestrial terminal equipment are described in greaterdetail in connection with the diagram of FIG. 4 . The routines mayinclude a terminal status check routine, a submarine cable use caseroutine, and so on. It should be understood that the routines describedherein are merely examples, and in other examples, certain steps may beadded, subtracted, replaced or reordered.

At block 410, a supervisory signal is transmitted from a first terminalof the terrestrial optical network. The supervisory signal may betransmitted through an optical cable to one or more adjacent nodes ofthe first terminal. The supervisory signal may be an OSC signal, an OTDRsignal, or another signal through which the first terminal may becapable of monitoring performance of the optical network.

At block 420, the first terminal determines whether the supervisorysignal is transmitted back to the first terminal. This may involvereceiving signals at one or more input communication ports of the firstterminal, processing the received signals, and identifying one or moreof the received signals as being the same as a previously transmittedsupervisory signal. In the absence of the supervisory signals beingreceived at the first terminal, such as after passage of a predeterminedduration of time, or after receiving an acknowledgment signal indicatingthat the transmitted supervisory signals were received at another nodeof the optical network, it may be determined that the supervisory signalwas not transmitted back to the first terminal.

If it is determined that the supervisory signal was not transmitted backto the first terminal, then operations continue at block 430, at whichthe first terminal determines that the supervisory signal wastransmitted to a second terminal, which may be another terminal of theterrestrial optical network connected to the first terminal. In thiscase, it may be determined that future optical signals transmitted tothe same node may be configured as terrestrial optical signals. Forinstance, this may involve transmitting the optical signals at apredetermined power level or without adding attenuation to the opticalsignals before transmission.

Alternatively, if it is determined that the supervisory signal wastransmitted back to the first terminal, then operations continue atblock 440, at which the first terminal determines that the supervisorysignal was rerouted or looped back to the first terminal by an OCIinterfacing the terrestrial optical network to a submarine cable of anearby submarine optical network.

In response to the determination at block 440, the first terminal, atblock 450, may initiate a submarine cable use case. Initiating thesubmarine cable use case may involve setting or changing one or moreconfigurations of the first terminal in order to accommodatecommunication between the first terminal and the nearby submarineoptical network through the OCI.

In some examples, initiating the submarine cable use case may involveinitiating a power reduction program 452. The power reduction programmay maintain power levels of transmissions to the OCI and submarinecable at or below a predetermined power level. The predetermined powerlevel may be determined according to specifications and guidelines forsubmarine cables, such as safety guidelines. In the case oftelecommunications, optical networks generally adhere to the safetyguidelines for Class 1M lasers. In situations where a power level of thecommunication signal is above the predetermined power level, the powerreduction program may cause a power level of the communication signal tobe reduced.

In some examples, initiating the submarine cable use case may involveupdating a travel distance between the first terminal and the OCI 454.Typically, supervisory signals transmitted between nodes of theterrestrial network travel between a transmitting node and a differentreceiving node, and the travel distance between the transmitting nodeand the receiving node can be derived from the elapsed time that thesignal travels. However, in the case of a supervisory signal transmittedto an OCI and then looped back to the transmitting node, the traveldistance of the signal is actually double the distance between thetransmitting node and the OCI. Therefore, in order to correctly derivetravel times between a transmitting node and an OCI, a distance betweenthe transmitting node and OCI may be halved. Determining to halve thedistance may be accomplished through a configuration at the firstterminal, whereby when the configuration is active, a travel time of thesupervisory signals transmitted from the first terminal to the OCI maybe evaluated based on have the halved travel distance.

In some examples, initiating the submarine cable use case may involveupdating an actual loss or attenuation of the supervisory signal betweenthe first terminal and the OCI 456. Typically, for supervisory signalstransmitted between nodes of the terrestrial network, an amount ofsignal loss experience between the transmitting node and the receivingnode can be detected by determining a property the signal, such as thesignal's power level, at each of the transmitting node and the receivingnode. However, in the case of a supervisory signal transmitted to an OCIand then looped back to the transmitting node, since the signal travelsdouble the distance, it is likely to experience double the losses duringtransmission. Therefore, in order to correctly derive actual lossesexperienced by the supervisory signals between a transmitting node andan OCI, the measured losses at the transmitting node may be halved.Determining to halve the measured losses may be accomplished through aconfiguration at the first terminal, whereby when the configuration isactive, the measured losses are halved in order to derive an estimate ofthe actual losses experienced in a single trip from the first terminalto the OCI.

The operations of the example routines 400 of FIG. 4 may be conductedduring an installation of the OCI. In other words, the first terminalmay initially determine, at a time of installation of the OCI or of thefirst terminal, the presence of the OCI, and may initialize its settingsto correctly and monitor the OCI, to transmit communication signals tothe OCI in adherence with submarine cable guidelines, or a combinationthereof. After this initialization, operations may continue based on theinitialized configurations. In some instances, the first terminal may becapable of regularly or continuously monitoring the looping back ofsupervisory signals, meaning that if the signals are not looped back orif an acknowledgement is signal is received at a future time, the firstterminal may determine to update its settings based on the detectedpresence of a second terrestrial terminal in place of the OCI.

Since the configuration operations are carried out from a terrestrialterminal that is remote from the OCI, and are not carried out at the OCIitself, it should be recognized that the installation of the terrestrialterminal may be performed by an ordinary technician, even though theterminal is being installed adjacent to an OCI interfacing a submarineoptical network. By comparison, when SLTE is required to be installedadjacent to an OCI to interface terrestrial and submarine opticalnetworks, a technician specially trained for installing SLTE isrequired.

As a result, terrestrial and submarine optical networks can beinterfaced with one another with standard “terrestrial-grade”terrestrial terminal equipment and without requiring specialized ordedicated terminal equipment and furthermore the installation of thestandard terrestrial terminal equipment can be performed by ordinary“terrestrial-grade” service technicians. This avoids the expensive coststypically associated with both specialized SLTE hardware and withinstallation by “white-glove” specialty technicians.

Additionally, the use of standard terrestrial terminal equipment inplace of SLTE means that all terminals included in the optical networkhave the same terminal equipment. This allows for a single SKU to beused to track all terminal equipment, which in turn saves considerabletime and hassle, as well as expenses, for those responsible for trackingand maintaining the optical network hardware.

Although the technology herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent technology. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present technology as defined by the appended claims.

Most of the foregoing alternative examples are not mutually exclusive,but may be implemented in various combinations to achieve uniqueadvantages. As these and other variations and combinations of thefeatures discussed above can be utilized without departing from thesubject matter defined by the claims, the foregoing description of theembodiments should be taken by way of illustration rather than by way oflimitation of the subject matter defined by the claims. As an example,the preceding operations do not have to be performed in the preciseorder described above. Rather, various steps can be handled in adifferent order, such as reversed, or simultaneously. Steps can also beomitted unless otherwise stated. In addition, the provision of theexamples described herein, as well as clauses phrased as “such as,”“including” and the like, should not be interpreted as limiting thesubject matter of the claims to the specific examples; rather, theexamples are intended to illustrate only one of many possibleembodiments. Further, the same reference numbers in different drawingscan identify the same or similar elements.

1. An open cable interface configured to connect a submarine cable to aterrestrial cable of an optical network, the open cable interfacecomprising: a first optical path configured to provide firstcommunication signals from the optical network to the submarine cable;and a second optical path configured to provide second communicationsignals from the submarine cable to the optical network, wherein thefirst and second communication signals are within a first frequencyband; and a first filter positioned on the first optical path andconfigured to: pass the first communication signals; and filter outsecondary signals from the terrestrial cable, wherein the secondarysignals are within a second frequency band that does not overlap withthe first frequency band.
 2. The open cable interface of claim 1,wherein the second frequency band includes at least one of 1510 nm or1610 nm.
 3. The open cable interface of claim 1, wherein the firstfilter is a wavelength division multiplexing filter.
 4. The open cableinterface of claim 1, wherein the secondary signals include an opticalsupervisory channel signal.
 5. The open cable interface of claim 1,wherein the secondary signals include an optical time-domainreflectometry signal.
 6. The open cable interface of claim 1, furthercomprising a second filter positioned on the second optical path andconfigured to pass the second communication signals from the submarinecable to the terrestrial cable, wherein the first and second filters areconfigured to loop the secondary signals received from the terrestrialcable back to the terrestrial cable.
 7. The open cable interface ofclaim 1, further comprising a first variable optical attenuatorpositioned on the first optical path between the first filter and thesubmarine cable and configured to adjust a power level of the firstcommunication signals without affecting a power level of the secondarysignals.
 8. The open cable interface of claim 1, further comprising asecond variable optical attenuator positioned on the second optical pathbetween the second filter and the submarine cable.
 9. The open cableinterface of claim 1, wherein the open cable interface is configured toconnect to a terrestrial transmission equipment having a same stockkeeping unit as other equipment included in the optical network that donot interface submarine cables.
 10. The optical network of claim 9,wherein the terrestrial cable has a same stock keeping unit as otherterrestrial cables included in the optical network.